The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
In a satellite-based positioning system (sometimes also referred to as a Global Navigation Satellite System (GNSS)), such as the U.S. Global Positioning System (GPS), the Russian GLObal NAvigation Satellite System (GLONASS), the European Galileo Navigation System (GALILEO), or the Chinese BeiDou-2 Navigation System (BDS), each active satellite within a satellite constellation broadcasts information including almanac data of the entire satellite constellation and ephemeris data of the broadcasting satellite. Almanac data are usable for determining rough positions of all satellites in the system. Ephemeris data are usable for determining a more accurate position of the broadcasting satellite than the corresponding rough position determined based on the almanac data. A position aware device, such as a satellite positioning receiver, can determine its position based on navigation signals received from various satellites and the positions of these satellites.
Moreover, an indicator of the performance of a position aware device is the Time-to-First-Fix (TTFF). The TTFF measures how long it takes a position aware device to provide an estimated position after the positioning functionality is activated. In some applications, the TTFF depends on many factors, including how long the position aware device takes to obtain the suitable almanac data and ephemeris data. However, receiving a complete set of almanac data and ephemeris data from a satellite is usually a time consuming task and susceptible to transmission losses caused by the atmosphere and/or obstructions. In an example, it takes a GPS receiver at least 30 seconds to receive one GPS message frame from a satellite, which includes a complete set of the ephemeris data and only 1/25 of a complete set of the almanac data.